This application is a continuation-in-part of U.S. patent application Ser. No. 203,746 entitled "Scan Converter System" and filed on Nov. 3, 1980, abandoned.
In ultrasound equipment using a phased-array transducer for producing images of a cross-section of the heart or other organs of a patient, the transducer is periodically pulsed so as to transmit an acoustic wave into the body. During an interval following each pulse, the array is focussed outwardly along a radial line of a sector so as to scan the line and translate the acoustic echoes received from body structure on that line into an analog voltage signal. A straightforward way of displaying this data is to deflect the electron beam of a cathode ray tube along corresponding radial lines and modulate its intensity with the analog voltage signal, but this is highly objectionable because of the voids between the radial lines that increase with range. In an attempt to overcome this problem, the analog voltage signal for each radial line is sampled at uniformly spaced points and each sample is reproduced at the nearest one of display points that are arranged in orthogonal rows and columns. As a result of not filling in all the voids, this technique creates a moire pattern. The moire has been reduced by techniques such as reproducing at a display point that is a void the same brightness that was produced at an adjacent display point, but this introduces artifactual boundaries or discontinuities into the image that are highly objectionable.
These problems are entirely eliminated by the invention described and claimed in the patent application referred to because all display points are provided with interpolated data values so as to constitute a full reconstruction of the image. The general manner in which one specie of the invention performs this function will now be explained by reference to FIG. 1 which illustrates the relative location of two radial lines R.sub.O and R.sub.I in a field of display points, x, that are arranged in rows having a separation K.sub.y that are orthogonal to columns having a separation K.sub.x. The analog signals along each radial line are sampled so as to produce a data sample S.sub.O0 at the origin of the radial line R.sub.O and data samples S.sub.O1 through S.sub.O8 that are respectively located where R.sub.O intersects arcs A.sub.1 through A.sub.8 that are concentric with the origin of the radial lines and uniformly spaced by a dimension s. Similarly, data sample S.sub.I0 is at the origin of the radial line R.sub.I and the data samples S.sub.I1 through S.sub.I8 are respectively located where R.sub.I intersects the arcs A.sub.1 through A.sub.8. The data samples for R.sub.O and R.sub.I are retained in memory while the data samples for the next radial line R.sub.D are being received and placed in the memory.
During the receipt of data from the radial line R.sub.D, all the display points between R.sub.O and R.sub.I are addressed in sequence such as indicated by the dash-dot line. As each display point is addressed, the data samples surrounding it are obtained and an interpolated data value to be displayed at that display point is derived from these data samples in the following way. Consider the display point DP located at the end of a radial line R. The radial distance of DP is determined, and if K.sub.y and K.sub.x are expressed in terms of s and are not greater than s, the fractional part of the radius will be RERR' and will also be the ratio, RERR, of the distance between the arc A* on which DP is located and the arc A.sub.2 to the arc separation s. RERR is then used to derive a first intermediate interpolated data value i.sub.O23 at the intersection of A* and R.sub.O from data samples S.sub.O2 and S.sub.O3 on R.sub.O. RERR is also used to derive a second intermediate interpolated data value i.sub.I23 from the data samples S.sub.I2 and S.sub.I3 on R.sub.I at the intersection of A* and R.sub.I.
The ratio .theta.ERR of the angle .theta.ERR' between R.sub.O and R to the angle .DELTA..theta. between R.sub.O and R.sub.I is determined and used in interpolating the first and second intermediate interpolated data values, i.sub.O23 and i.sub.I23, so as to derive the final interpolated data value for the display point DP.
As explained in the patent application referred to, RERR and .theta.ERR are each derived by a process involving the recursive addition of certain constants for each step from one display point to the next, and counters are used to derive the appropriate data samples from the line memory. The values of RERR and the data samples such as S.sub.O2 and S.sub.O3 are applied to a ROM so as to derive a first intermediate interpolated data value such as i.sub.O23 and RERR and data samples such as S.sub.I2 and S.sub.I3 are applied to another ROM so as to derive a second intermediate interpolated data value such as i.sub.I23. The values i.sub.O23 and i.sub.I23 and .theta.ERR are applied to a third ROM so as to derive the final interpolated data value for a display point such as DP.
As more particularly described in a continuation-in-part of the patent application referred to, which was filed on Nov. 2, 1981, Ser No. 317,081 all of the data samples of a sector may be stored in memory and ROMs may be used to select the appropriate samples, derive the same first and second intermediate interpolated data values, and derive the final interpolated data value for a display point in response to signals indicating its coordinates by row and column.